This proposal describes a research plan into the role of the Hedgehog/Gli transcription factors in normal hematopoiesis and leukemia and a training program to develop the principal investigator, Dr. Akil Merchant, from a junior faculty member into an independent physician-scientist. Dr. Merchant studied normal hematopoiesis while a resident in internal medicine. As a medical oncology fellow in the laboratory of Dr. William Matsui, Johns Hopkins University, he focused on the role of the Hedgehog (Hh) pathway in hematopoiesis and leukemia. Dr. Matsui was the first investigator to report that Hh signaling regulates cancer stem cells in multiple myeloma and is a recognized expert in the field. Dr. Merchant started on the faculty at Johns Hopkins in March 2010 in the Department of Hematology and was promoted to Assistant Professor in March of 2011. This grant will support his goal of becoming a laboratory based translational researcher in hematologic malignancies. The Hedgehog pathway is a promising new target for cancer therapy. Previous studies in normal hematopoiesis and leukemia have focused primarily on the upstream modulators of the pathway Patched (Ptch) and Smoothened (Smo), and have led to contradictory conclusions. Hh pathway output is ultimately determined by the combinatorial effects of the three downstream Gli transcription factors: Gli1, Gli2 and Gli3. Our understanding of Hh function is complicated by functional redundancy between Gli1 and Gli2, context dependent activator or repressor functions for Gli2 and Gli3, and the convergence of other oncogenic signaling pathways on the Gli factors. Direct inhibitors of the Gli factors have promise as anticancer agents, however, a better understand of their function is needed to effectively develop them into therapies. Using mice with a genetic deletion of Gli1, Gli2, or Gli3, the proposed research will examine the roles of each transcription factor in normal hematopoiesis and leukemia. The aims of this proposal are: 1) Determine the effect of (a) Gli activator (Gli1/Gli2) loss and (b) Gli3 loss on normal hematopoiesis, 2) Determine the requirement for Gli activator function (Gli1/Gli2) in (a) BCR-abl induced acute leukemia and (b) the progression of Flt3-ITD induced myeloproliferative disease to acute leukemia, 3) Determine if (a) Gli3 functions as a tumor suppressor in leukemia (b) loss of Gli3 confers self-renewal to bone marrow committed progenitors (c) restoration of Gli3 expression sensitizes cells to Smo antagonists. The investigators hypothesize that a more sophisticated understanding of the role of individual Gli factors in cancer will aid in optimally selecting patients for treatment with Hh inhibitors, help predict the hematopoietic toxicities of H inhibitors, and guide the design drugs that can directly target the Gli factors.